1. Field of the Invention
The present invention relates to catheters or cannulae to be used during medical procedures where it is desirable to create a cool or warm environment selectively and more specifically to protect the brain. Hypothermia has been suggested as one of the most potent approaches to both minimizing and therapeutically treating ischemic brain injury. Over the past decade there has been an increased interest in the use of hypothermia as a means for creating a neuroprotective environment during cardiac, cerebrovascular and neurologic surgery, as well as for acute stroke therapy and traumatic head injury. Although not all of the etiological mechanisms are fully understood, hypothermia confers a neuroprotective environment by (1) reducing cerebral metabolism, making the brain more tolerant of reduced blood flow; (2) decreasing excitatory amino acids; (3) stabilizing the blood brain barrier and (4) decreasing heat shock proteins after induced brain injury.
Even though the benefits of cerebral hypothermia have been documented, the widespread use in surgery, neurosurgery, trauma, closed head injury and stroke has not been readily adopted. This lack of adoption is based in large part because of the complications associated with the systemic nature of achieving the hypothermic condition. For example, in cardiac surgery perfusing the entire patient with hypothermic blood from an extracorporeal bypass unit is the common method for obtaining cerebral hypothermia. Using external heat exchangers such as those described in U.S. Pat. No. 5,997,816 to McIntosh et al. and U.S. Pat. No. 5,421,405 to Goddin et al., the teachings of which are hereby incorporated by reference, total body hypothermia can be induced. This modality of hypothermia carries potential risks, including arrhythmias, infection and coagulopathies. To avoid these complications, there has been a trend toward performing cardiopulmonary bypass at normothermic temperatures and using hypothermia in a very selective group of procedures including aortic arch dissections and heart lung transplantation. In addition, topical cooling in the form of ice baths, cooling helmets and cooling blankets have been proposed for cooling the patient""s brain in cases of severe head trauma and stroke, however these technologies are inefficient and take too long to be truly effective for rapid cooling of the brain core.
Therefore, what has been needed and heretofore unavailable, is a method and apparatus for selectively cooling the brain apart from the rest of the body in any medical procedure where an ischemic event may or has occurred. By employing novel pumping and cooling devices that require minimal priming volume, along with new methods for controlling patient temperature selectively, the shortcomings of previous medical devices can be overcome. Such methods and devices would offer clinicians significant advantages in managing patients at high risk of neurologic damage, thereby improving outcomes. Furthermore, selective cerebral hypothermic therapy can be used in beating heart cardiac surgery, minimally invasive cardiac surgery, open chest heart surgery, traumatic brain injury, neurosurgery and stroke. The methods and apparatus can be used to extend the therapeutic window for other interventions, can enhance the effects of pharmacological and other co-therapies, as well as provide a neuroprotective environment for aneurysm clipping, coil delivery and other forms of interventional neurology and cardiac surgery.
2. Description of the Background Art
U.S. Pat. No. 5,971,979 to Joye et al. describes a method of delivering compressed cryogenic fluid to the interior of a balloon catheter for selectively freezing a patient""s vasculature. U.S. Pat. No. 6,019,783 to Philips, U.S. Pat. No. 4,860,744 to Johnson et al. and U.S. Pat. No. 4,483,341 to Witteles describe thermoelectric cooling systems. U.S. Pat. No. 5,901,783 to Dobak, III describes a cryogenic heat exchanger. U.S. Pat. No. 5,275,595 also to Dobak, III describes a closed cycle cryosurgical instrument. U.S. Pat. No. 5,957,963 to Dobak, III describes a method and apparatus for selective organ hypothermia. U.S. Pat. No. 8,837,003 to Ginsburg describes a method and apparatus for controlling a patient""s body temperature by in situ cooling of blood. U.S. Pat. No. 5,794,629 and 5,908,407 to Frazee contemplate the use of catheters for delivering blood flow to selective organs by retrograde perfusion. U.S. Pat. No. 5,820,593 and 5,906,588 to Safar et al. describe methods and apparatus for selectively cooling body organs. Cryogenic fluid sources are described in U.S. Pat. No. 5,644,502 to Little and micropumps are disclosed in U.S. Pat. No. 4,919,647 to Nash, U.S. Pat. No. 5,911,685 to Siess et al., U.S. Pat. No. 5,507,629 to Jarvik, U.S. Pat. No. 4,625,712 and 5,695,471 to Wampler, WO 99/02204 to Aboul-Hosn and WO 99/59652 to Aboul-Hosn. The full disclosures of each of the above US patents are hereby incorporated by reference in their entirety.
In keeping with the foregoing discussion, the present invention provides novel cooling and perfusion devices, which can be used in a variety of medical procedures, including, but not limited to: stroke, closed head brain injury, trauma, rescusitation, and all forms of general surgery and cardiac surgery. The methods and devices of the present invention include in-line heat exchangers as well as in-line intravascular blood pumps, which reduce priming volume and are compact in design.
In one illustrative embodiment, the present invention provides a fluid transport system, a flexible elongate catheter, and a temperature regulation assembly. The catheter is comprised of three tubular bodies/members, which extend in a substantially coaxial configuration. The tubular members are collectively referred to as a shaft assembly and may be manufactured from metals, alloys, flexible thermoplastic materials, thermoplastic elastomers or thermoset elastomers. More specifically, suitable materials for the shaft assembly include, but are not limited to, PEBAX, PVC, PET, polystyrene, polyvinylchloride, polyurethane, polyethylene, polypropylene, polyamides (nylons), copolymers, polyesters, silicone, latex, and combinations thereof, as well as braided, coiled or counterwound wire reinforcement or filament reinforced composites. Alternatively, or in combination therewith, the shaft assembly or any one of the tubular members may be made of thin walled metallic tubing or hypotube constructed of materials such as stainless steel, platinum, titanium, nitinol alloys and Cobalt alloys such as Elgiloy and Carpenter MP 35.
The innermost tubular member has a delivery lumen that is sized and configured to deliver a heat exchanging medium. There are a variety of heat exchanging mediums that are well known in the art including, but not limited to: water, blood, saline and compressed refrigerants, such as freon, liquid nitrogen or nitrous oxide. A second tubular member has a second lumen/return lumen that is sized and configured to serve as a return for the heat exchanging medium. The first tubular member and the second tubular member together comprise a heat exchanging apparatus that extends at least in part through the outermost tubular member/third tubular member. The outermost tubular member serves as a housing for the heat exchanging apparatus and has an internal lumen/fluid lumen which serves as a fluid lumen. The fluid lumen is isolated from the return lumen creating a heat exchanging interface that facilitates heat exchange between the fluid lumen and the return lumen. Fluid such as blood, water, saline, lysing agents, clot dissolving pharmacological agents, glutamate antagonists, calcium channel blockers, salt based solutions or any other fluid composition or combination may travel over the surface of the second tubular member through the fluid lumen where temperature can be controlled and heat transfer occurs.
A guidewire lumen is also provided to facilitate the insertion of a steerable guidewire. In alternative embodiments, the guidewire lumen may be incorporated into one of the other lumens to create a more compact design, or a fixed guidewire may be attached to the distal end of the catheter shaft, as is well known in the art. Furthermore, the guidewire lumen can serve to facilitate the insertion of other medical devices or microcatheters such as carotid stent catheters, aneurysm clip catheters, dilation catheters, diagnostic catheters, coil catheters, aneurysm catheters or occlusion catheters which access the patient""s vasculature through perfusion ports or a specific access port designated along the length of the catheter shaft, which is sized and configured for optimal access, or out the distal opening.
The innermost tubular member may have a plurality of outputs representing expansion orifices that are located along the length of the shaft. The expansion orifices are sized and configured for allowing the expansion of the heat transfer material into the lower pressure region of the second tubular member. The outputs may be created by mechanically penetrating the surface of the hypotube, or alternatively may be formed by using lasers or by chemical etching. Preferably, the spacing between the orifices, as well as the size and shape are selected to allow for the appropriate expansion of the heat exchanging medium to provide the appropriate temperature regulation under certain pressure conditions. In one preferred embodiment, the spacing between the orifices is selected such that uniform cooling along the length of the shaft is possible. The outputs may be located directly across from one another or alternatively may be staggered along the length of the first tubular member.
In one illustrative embodiment, compressed nitrous oxide is delivered through the delivery lumen where expansion occurs upon exiting the outputs. The nitrous oxide vaporizes as it expands, cooling the second tubular member to facilitate heat transfer as blood or other fluid flows over the cold surface.
Alternatively, or in addition thereto, the distal end of the inner tubular member may also be configured to have an integral heat transfer bellows. In addition, or alternatively the distal end of the inner tubular member may be coupled to a Joule-Thomson valve. Furthermore, only one distal output with or without the aforementioned heat transfer bellows or Joule-Thomson valve may be necessary to accomplish desired results.
In another illustrative embodiment cold or warm water may be used as the heat exchanging medium. A closed circulation system can be maintained by circulating the water through the catheter by maintaining a higher pressure on the input of the inner tube and a lower pressure on the output of the second tubular member to create the desired flow of heat exchanging medium through the heat transfer system.
The second tubular member can be formed from a variety of materials as discussed above and in a preferred embodiment a high thermal conductivity metal is used to enhance optimum heat transfer between the surface of the second inner tube and fluid communicating within the fluid lumen of the outer tubular member. Examples of materials having high thermal conductivity include copper, gold, nitinol, platinum iridium, aluminium and stainless steel. In addition, the above listed materials may be coated to ensure hemocompatibility. Furthermore, the second tubular member may be constructed to have fins or other means for enhancing the surface area and corresponding heat transfer ability of the second tubular member. For example, in one preferred embodiment the second tubular member may be constructed of a substantially cylindrical tube having a plurality of substantially parallel longitudinal corrugations. Each corrugation increases the total amount of surface area capable of heat transfer. Blood or other fluid flows over the surface of the exterior fluid flow channel and the heat exchanging medium is circulated through the interior return channels.
A first tube fitting is connected by known means to the output of a temperature regulation assembly for delivering the heat exchange material to the delivery lumen. A second tube fitting is connected by known means to the input of the temperature regulation assembly serving as a return for the heat exchange material to the temperature regulation assembly. In an alternative embodiment, the return lumen may open to atmosphere or to a separate holding chamber, rather than being recirculated through the temperature regulation assembly, as would be typical in a closed cycle.
A fluid transport system has an input and an output in fluid communication with the fluid lumen of the catheter. An external pump is coupled to a tube fitting where fluid can be communicated from the patient""s peripheral artery or vein. The term external pump is intended to describe generically all pumps that reside outside of the vasculature of the human body. External pumps may be in the form of centrifugal pumps, peristaltic pumps or roller pumps, as are commonly associated with cardiopulmonary bypass machines. In addition, mechanical hand pumps that are operated through manual pumping mechanisms, incremental squeeze pumps, diaphragm pumps or displacement pumps for emergency resuscitation or trauma can be used. In alternative embodiments, micropumps or axial pumps can be used which are located within the catheter body or within the tubing circuit, but outside of the patient""s vasculature, thereby reducing priming volume. Alternatively, in another illustrative embodiment internal pump(s) can be used. The term internal pump is meant to describe generically pumps with impellers or auger type pumps that reside within a patient""s vasculature. The fluid transportation system has a first luer connector connected to a fluid composition altering source and a second luer connector or other suitable fitting capable of fluid sampling or for monitoring pressure, temperature or chemical composition.
A fourth tube connector is in fluid communication with the guidewire lumen having a hemostasis valve, a Touhy-Borst fitting or other suitable fitting capable of facilitating the insertion of guidewire(s) or other medical instruments through the guidewire lumen.
Another embodiment of the present invention, configured for selectively cooling tissue, comprises a catheter, a fluid transport system and a temperature regulation assembly. The catheter shaft is comprised of a delivery lumen that is sized and configured to deliver a heat exchanging medium at least in part through the length of the catheter shaft. A return lumen is sized and configured to serve as a return for the heat exchanging medium. The delivery lumen and the return lumen together serve as a heat exchanging apparatus that extends at least in part through the catheter shaft. The catheter shaft serves as a housing for the heat exchanging apparatus allowing for the selective cooling or heating of a fluid within a catheter body. The fluid transport system has an internal pump connected to a power lead extending through the catheter shaft to a remote power source. In alternative embodiments, a separate lumen may be provided to house the power lead or alternatively the power lead may be integrally formed within the catheter shaft where no separate lumen is required. Alternatively, the power source may reside adjacent to the internal pump using battery power or the like where no power lead is necessary.
The internal pump communicates autologous blood from a vessel to a fluid lumen where the blood travels over the surface of the heat exchanging interface to cool or warm the blood. Fluid such as blood, in addition to other additives such as thrombolytics, lysing agents, clot dissolving pharmacological agents, glutamate antagonists, calcium channel blockers, salt based solutions or any other fluid composition or combination will travel over the surface where temperature can be controlled and heat transfer occurs.
A guidewire lumen is also provided to facilitate the insertion of a steerable guidewire. In alternative embodiments the guidewire lumen may be incorporated into one of the other lumens to create a more compact design where a fixed guidewire may be attached to the distal end of the catheter shaft, as is well known in the art. Furthermore, the guidewire lumen can serve to facilitate the insertion of other medical devices or microcatheters, such as carotid stent catheters, aneurysm clip catheters, dilation catheters, diagnostic catheters, coil catheters or occlusion catheters which access the patient""s vasculature through perfusion ports or a specific access port designated along the length of the catheter shaft, which is sized and configured for optimal access, or out the distal opening where the device is mechanically similar to a guide catheter.
A manifold is attached to the catheter shaft and has fittings coupled to the various lumens of the catheter shaft. A fitting is connected by known means to the output of a temperature regulation assembly for circulating the heat exchange material to the delivery lumen. A compressed refrigerant such as liquid nitrogen or nitrous oxide is used to deliver the heat exchange material to the delivery lumen. In another illustrative embodiment cold water is used. A second fitting is connected by known means to the input of the temperature regulation assembly as a return for the heat exchange material to the temperature regulation assembly. In alternative embodiments the return lumen may open to atmosphere or to a separate holding chamber rather than being recirculated through the temperature regulation assembly, as would be typical in a closed cycle circuit.
A hemostasis valve, Touhy-Borst fitting or other suitable fitting capable of facilitating insertion of other medical devices or instruments is in fluid communication with the guidewire lumen. Furthermore, a luer connector extending from the Touhy-Borst fitting is configured for measuring flow, pressure, temperature and chemical composition by way of ports or the end opening.
The catheter system of the present invention is multifunctional and is adapted to perform effectively in a variety of medical situations. For example, in an emergency situation, such as stroke, trauma, resuscitation or traumatic brain injury the catheter is designed for ease of insertion into a peripheral vessel for rapid cooling of the brain or warming the body or a combination of both. Alternatively, during an elective cardiac surgery including traditional stopped heart, beating heart or minimally invasive cardiac surgery or neurosurgery the catheter is effective for rapid cooling of the brain to create a cerebral protective environment. Methods for introducing the catheter include percutaneous insertion, arterial cutdown, Seldinger technique over a guidewire, as well as an aortotomy with a purse string suture. The catheter can be introduced through any peripheral access vessel including the subclavian, radial, iliac, femoral or brachial artery or alternatively through an intercostal space, median stemotomy minithoracotomy or left thoracotomy. Once inserted, the catheter is navigated into an operative position until blood perfusion ports are proximate or adjacent to the arch vessels. The brain is cooled selectively from the rest of the body rapidly and efficiently, as the internal pump directs blood over the heat exchanging interface where it is cooled along the length of the catheter shaft. The blood is cooled to the optimal temperature and exits out the perfusion ports where cooled fluid is delivered to the cerebral circulation in an efficient manner.
In embodiments where the catheter is navigated into the operative position over a guidewire and additional intervention is necessary, the guidewire is removed through a Touhy-Borst fitting and another medical instrument or device is inserted therethrough. In one preferred embodiment a carotid stent catheter is employed having an additional guidewire fitting and inflation fitting. The medical device may access any number of organs or vessels and therefore any number of ports may be implemented to facilitate the desired procedure. For example, if the heart is the target organ the end port may be the optimal port to reach the heart in peripheral approaches. Alternatively, if the cerebral vasculature or carotid arteries are the target area then side ports, which also serve as perfusion ports, might be the most desirable port(s) to use. In addition, in other alternative embodiments another port and or lumen designed especially for other medical devices can be implemented. Other medical devices which may be inserted through the catheter include angioplasty balloon catheters, stent catheters, atherectomy catheters, transmyocardial revascularization catheters, pigtail catheters, filters, in stent restenosis removal catheters, stent removal catheters, diagnostic catheters, angiogram catheters, carotid stent catheters, aneurysm clip catheters, coil delivery catheters, embolization therapy catheters, drug delivery catheters or secondary temperature regulation or measuring catheters or any other medical device.
In another embodiment of the present invention, an aortic isolator in the form of an expandable membrane or filter mesh is coupled to the distal portion of the catheter shaft. The expandable membrane is configured to have a top surface, a bottom surface, a proximal portion, a distal portion, a length and a width. The expandable membrane may be formed in a variety of configurations, however, in general, the expandable membrane will have an undeployed or collapsed state and a deployed or expanded state. In the collapsed state the expandable membrane is not substantially larger than the external diameter of the catheter shaft. In the expanded state, the membrane is configured to create two fluid flow paths, which optimize the cooling of the cerebral circulation. The expandable membrane may be deployed from an exterior surface of the catheter shaft, or it may be deployed from within a lumen in the catheter shaft or another catheter.
The expandable membrane has one or more biasing ribs or inflatable chambers, which serve a multiplicity of functions. In one preferred embodiment the inflatable chambers are in fluid communication with the delivery lumen of the heat exchanging apparatus. The heat exchanging medium is allowed to expand within the inflatable chambers, actuating the expandable membrane as well as cooling the inflatable membrane such that any blood residing within or flowing through the vessel that interfaces with the inflatable membrane becomes cooled. In a preferred embodiment, only the upper surface of the expandable membrane serves as a heat exchanging interface, that is, the surface facing toward the arch vessels is configured for cooling blood within the vessel. Blood traveling downstream which interfaces with the lower surface of the expandable membrane is kept normothermic by thermally insulating the lower surface of the membrane to prevent systemic cooling.
In another illustrative embodiment of the present invention the catheter shaft is deployed within a patient""s aorta having an occluding member located near the distal end of the catheter shaft for stabilizing the catheter in an operative position. In addition, the catheter is configured for delivering a treated fluid to the cerebral circulation and can selectively cool cerebral tissue through an internal heat exchanger having an internal impeller pump.